Rain and Flood Event March 2012

All models are pointing to a significant event in southeastern to eastern NSW and eastern Victoria. In fact, anywhere from central Australia through the south eastern states a cloud band is streaming dumping the heavy rainfalls particularly with thunderstorms. Flood watches and warnings are in place in Victoria and expected flooding are also anticipated in eastern NSW.

For me, the most significant component is the expected flooding of the Hawkesbury Neapean River system which although is not the major part of the event but it is the first river flooding of this significance in over 20 years!

Although not as widespread and as intense as the previous year’s La Nina episode, it seems there is some similarity. Check this out:

As an example, Ivanhoe Post Office in southern New South Wales recorded a 7-day total of 294.1 mm, equivalent to 10 times the monthly mean of 28 mm and almost equal to its annual mean rainfall (306 mm), i.e., nearly a year’s worth of rain. Many stations in the affected region set record high rainfall totals for periods ranging from 3 to 7 days.

And this:

The rainfall event is remarkable in that record high daily accumulations (for any month) were recorded over a large area. New South Wales recorded its 2nd, 3rd and 4th highest statewide daily rainfall totals on record for March, with a 7-day statewide rainfall average of 123.9 mm ranking as the equal highest for the state for any month (equal with 123.9mm from 7–13 January 1974). For the Murray-Darling Basin and the southern part of New South Wales, including northern Victoria, this event was the wettest 7-day period on record for any month. The accumulated rainfall in the Murrumbidgee catchment for the 7–days of 202.6 mm was nearly double the previous highest on record (114.7 mm for 1–7/2/2011 followed by 102.1 mm for 7–13/4/1974; Table 6). In this context the event is one of the most extreme multi-day rainfall events in southeast Australia’s history.

And of course:

The highest 7–day accumulated rainfall total during the event was 525.0 mm recorded at Mount Buffalo. The exceptional rainfall caused widespread major, moderate and minor flooding across southeastern New South Wales as well as northern and eastern Victoria.

These sort of rainfalls given the southern location is up there with some of the North Coast style rainfalls.

Incredible – have we returned back to the 1950’s and 1970’s style episodes?

I guess this reflects the similarities I had hinted in my previous post:

Historical data reveals a tendency for heavy summer rainfall in southeast Australia to occur while under the influence of La Niña, with similar rainfall events having occurred in the past. Notable events include 24 February to 1 March 1939 and 16 to 20 March 1950 (Figure 12), with widespread heavy rain across northern Victoria and southern New South Wales associated with slow-moving low pressure troughs. The recent rain pattern is also similar to several widespread rain events associated with low pressure troughs during the 2010/2011 La Niña event, most particularly in southern NSW during early February 2011. Comparison with these previous events highlights general similarity, but also underscores that the recent rainfall event is the most extreme for southern New South Wales in terms of extent of heavy rainfall and peak rainfall totals.